The present invention relates to methods for filing apertures with crystalline material and specifically to the filling of a plurality of apertures in a single sheet.
Various radiation conversion screens, such as those which convert x-rays to visible light, are fabricated by forming an array of apertures in a glass sheet. These apertures are then filled with a phosphorescent material which will convert the x-rays to visible light. The phosphorescent material in each aperture must be as optically transparent as possible to enable the light generated within the aperture to radiate from the phosphorescent material. It is most desirable, therefore, that the phosphorescent material in each aperture have as close as a single crystalline structure as possible since any non-uniformity in the structure will impede the light transmission. When the phosphorescent material has a higher index of refraction than the glass sheet, each filled aperture forms a fiber optic element. This procedure for fabricating the conversion screen permits the sheet thickness and the element diameter to be selected for optimum resolution and sensitivity.
Recent technological advances have made it possible to form a glass sheet having a matrix of extremely small apertures. For example, glass sheets having a matrix of closely packed holes each ten microns in diameter are readily available. However, difficulty has been encountered when conventional manufacturing techniques were used to fill the tiny apertures with phosphorescent material. Heretofore, the phosphorescent material was melted on the sheet's surface by heating the entire sheet. Capillary action then drew the material into the apertures. Because of the relatively small size of the apertures, the molten crystalline material is rapidly cooled as it flows into each aperture and recrystallizes before the entire aperture is filled. When large screens are made, the filling is further complicated by temperature gradients across the sheet's surface. The molten crystalline material tends to flow to the cooler sections of the sheet resulting in an unequal filling of the apertures.